Electromagnetic vibrator



FORCE /N Sil/7481.5 l/N/ TQS R. B. coL'roN ET Al. 2,025,041` ELECTROMAQNETLIC vIBRA'roR Filed Mavrh 9. 1931 Dec. 24, 1935.

Patented Dec. 24, 1935 2,025,041 ELECTROMAGNETIC vnmli'ron Roger `B. Colton, Quarry Heights, Canal Zone,

and

Harold C. Mabhott, Fort Monroe, Va.

Application March 9, 1931, Serial No. 521,362 9 Claims, (CL 177-383) (Greuted'under the se t of March amended April 30, 1928A;v 37o 0.

'I'he invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to electro-magnetic vibrators..

The invention has for its objectimprovementin the operation of electro-magnetic 4vibrators in the matter of faithfulness, eiliciency and reliabil- 10 ity in conversion of sound ormechanical energy into electrical energy and in the conversion of electrical energy into sound or mechanical energy.

The' invention as regards one of its main features, is based on the fundamental idea that there l5 is in such vibrators, when properly arranged, a magnetic force tending to increase the armature displacement, which may, over the working range, be balanced to any desired extent and which may outside the working range be enormously over balanced by the mechanical force tending to decrease the armature displacement, furnished by a proper material inserted between the armature and core. Such being the case, net mechanical stiffness of any desired amount may be secured over the working range while outside that range net mechanical stiiiness may be made sumciently great to insure certainty and stability of operation. Y

In order that there shall be no confusion it will be here explained that the term mechanical still--- ness is to be taken to apply to the mechanical force of restitution while magnetic stiffness is to be taken to apply to the magnetic force of displacement, each being defined as the increase-of the corresponding force per unit movement of the vibrator armature.`

With the foregoing and other objects in view, the invention consists in the details of construction and combination of parts hereinafter set- 40 forth. an `embodiment thereof being illustrated in the accompanying drawingln which:

Figure 1 is a plan view of one form of device embodying the invention;

Figure 2 is a transverse sectionl on the line ,A-B

of Figure 1;

Figure 3 is a longitudinal section on the line C-D of Figure l;

Figure 4 is a schematic wiring diagram of the form of the invention' shown in Figures 1, 2, and

3; and.

. Figure 5 is a graph showing the manner in' which mechanical and magnetic factors ofl stiffness combine in the present and comparative devices.

Referring to Figures 1, 2, and 3, I is'a laminated core of magnetic material. The laminations are held together by the rods 2 which are upset at their ends in the manner customary in the art. The core is secured in place in the housing 3 by having its lower shoulders clamped bythe base l. 5

The base is secured to the housing by screws 5 and the jointis made pressure tight by the gasket i. Coils of insulated copper wire 1 and 8, are placed around the legs of the core. A soft rubberspacer N in the gap between the armature 9 and 1o the core I and cemented to both, provides the necessary armature mechanical stiffness. A soft rubber diaphragm I I is superposed upon the back of the armature and, extending under the diaphragm clamp I2, is compressed between the 15 diaphragm clamp and the housing when the screws l1 are properly tightened, and its outer periphery therefore serves the purpose of a gasket and renders the joint between the housing and diaphragm pressure tight. A groove as at I3 20 extending around the housing provides space for flow of the material at the edge of the diaphragm y and thereby assists in'keeping the diaphragm iiat. Thin spacers Il and I5 of soft rubber resting in shoulders lin the housing and abutting against the armature and secured by being clamped by the pressure of the diaphragm assist the spacer Ii and diaphragm I I to hold the armature in position, but without contributing materially to the amature mechanical stillness, which is provided by spacer I0. The amature is composed of laminated magnetic material and the laminations arev held together by rods I8. The stumngbox I8, the details ofwhich are omitted, provides a pres- A sure 'tight means whereby insulated connecting .35 wires (not, shown) may be brought into the housing, while the drilled and tappedfextrusion I9 provides means for evacuating the housing or lfilling it with compressed uid; and the needle valve screw 20 provides a means of preventing or controlling ingress or egress of fluid to orv from thehousing. AshasbeenstatedFigureiisa diagrammatic representation of a method of wiring up the device illustrated inFigures 1, 2, and 3. Referring` now to Figure 4, -2 I isa choke coil substantially passing onlyV steadycurrent; 22` is a battery furnishing current to coil 1 through the choke .coil 2|, and 2l is an electrical receiving appay ratus or an -electrical energy sink 4of desirable type, connected to coil 8.'v

Considering the device as described above,

sound pressure exerted on the diaphragm II is transmitted to @he armature 9 causing it to vibrate. Vibration of the armature causes the 55 rubber spacing sheet I 0 to expand and contract, thus increasing and decreasing the reluctance of the magnetic circuit formed by the core, the armature and the gap between the armature and core, and since the current through coil 1 pro vides a steady magnetomotive force the flux through the magnetic circuit varies in response to the vibration of the amature, inducing in coil 8 a voltage and in circuit 8-23 a current which actuates receiving device 23.

Conversely, if the receiving device 23 is replaced by a source of variable electromotive force, the consequent current will produce a variable iiux in the magnetic circuit and the armature will move due to the consequent variation of the force of attraction between the core and armature. The movement of the armature likewise causes a movement of the diaphragm and sound is emitted therefrom.

In the past in devices of this character the necessary restoring force has been supplied by spring action on the part of the diaphragm or by similar means. Under these conditions, it has been necessary to provide either an excessive mechanical stiffness or an excessive air gap or a very weak magnetic field to prevent adhesion of the armature to the core.

In the form of the present invention illustrated in Figures 1, 2, and 3 the restoring force is provided by the rubber sheet I0. Rubber has the characteristic that its coefficient of elasticity increases under increasing pressure; hence even though the device be subjected to very excessive forces the armature is always held away from the core and it is possible to use any desired physically obtainable value of the steady iiux, length of nonferrous gap and residual mechanical stiffness. This point will be understood by reference to Figure 5. Curve D shows qualitatively the manner in which the force of magnetic attraction varies with the length of the nonferrous gap. This force increases more and more rapidly as the nonferrous gap (plotted as abscissa) decreases. Curve A shows the force of repulsion when the armature is secured by a true spring of constant elasticity. In this case the armature assumes equilibrium at the normal operating point B where the two forces are in balance, and has a residual mechanical stiness in the vicinity of point B equal numerically to the difference of the ordinates of A and D divided by the difference between the corresponding abscissa and the abscissa of point B. However, if under the impulsion of any large force the armature reaches a point even slightly to the left of point C it will of necessity continue to decrease the nonferrous gap and freeze on the core, rendering the device inoperative, since the residual stiffness is now magnetic, i. e. the resultant force is henceforth away from B.

Now curve E represents the force of repulsion in a case when the armature and core are separated by a material that has a coeflicient of elasticity increasing with pressure. In this case the armature assumes equilibrium at the normal operating point F and as this is the only point of intersection of curves D and E there is no point of instability (residual stiffness always being mechanical) Further, by suitably dimensioning the spacing material it is apparent that the operating point can be moved at will along curve D. It is also true that by either suitably dimensioning the spacing material, or by selecting a material of suitable characteristics the curve E may be given almost any desired shape, and hence any desired constant residual mechanical stiffness may be secured over a wide working range of gap length, while very large residual mechanical stiffness is provided outside the working range. It will frequently be found best and most 5 convenient to shape curve E so that the residual mechanical stiffness is small but constant over a selected range each side of the operating point, beyond this range on the side of the core, i. e. on the side of decreasing nonferrous gap, in- 10 creases rapidly with decreasing nonferrous gap, and beyond this range on the side away from the core is at least as large as over the selected working range each side of the operating point.

It will be apparent to one 4familiar with the 15 art that curve E, having been determined by selecting and dimensioning of the spacing material, can be further altered by application to the armature of forces other than those supplied by magnetic action and by the elasticity of the spacing 20 material. For this purpose and since it is sometimes desirable, as when working at great depths in water. to provide a means of balancing in whole or in part or in excess outside pressure, the device is made pressure tight and the extrusion I9 fitted 25 with the needle valve 20 is provided so that iiuid may be introduced into or extracted from the device. If a light gaseous uid is used within the housing and the space within is large, addition or extraction of fluid has substantially no'eiect 30 on the shape of the stiffness curve, the only eect being to translate the curve parallel to itself along the gap length coordinate. However, if fluids having a high elastic coeilicient are used, or if the space within the housing is small, addition or extraction of fluid both displaces the mechanical stiffness curve and changes its shape.

In the form of the device shown in Figures l, 2, and 3, core losses have been reduced by laminating the core and armature, but this construction 4o it not always essential.

In order that there maybe no confusion, it is here explained that the term magnetic material as hereinbefore or hereinafter used should be taken to mean a material having magnetic 45A qualities similar to those of iron, and that the term nonferro should likewise be taken to mean not having the magnetic qualities of iron". When the construction of Figures. 1, 2, and 3 is used, and an excess of pressure isy used within 50 the housing, it may be advisable to cement or vulcanize the diaphragm Il to the armature, or other means, may be used, to prevent collection of iiuid between the armature and diaphragm and 4to insure contact between the'diaphragm and ar- 55 mature.

While it has been stated that the spacer 0 is cemented to the armature and to the core, such procedure is not essential if the armature is otherwise held in position by any means that 60 does not prevent the maintenance of the desired `armature residual mechanical stiffness curve, as

for instance by means ofv spacers I4 and I5. Cementing' of spacer I0 is, however, in general advantageous since contact of the spacer I0 with 65 both armature and core is thereby assured and at the same time the armature is held in position transversely to its operative movement.

As has been stated previously, curve E, Figure 5, may be shaped by the application of additional 70 forces other than those supplied by the spacing material. Suchv shaping by means of fluid pressure has already been discussed, but other means may be used. When such means of shaping the mechanical stiffness curve is used, one familiar 75 with the art will understand the proper procedure from the discussion previously given. 1-

I-Iereinbefore it has been stated that sheet I! may be of any elastic material whose coemcient ot elasticity increases with increasing pressure. It is intended, of course. that this process be reversible, i.e., that the coeilicient oi elasticity oi' the material shall likewise decrease with decrease oi pressure. In other words, sheet I may be composed of any elastic material having 'a coeiilcient of elasticity proportionate to pressure. Further, in order that there be no doubt or confusion, it is now stated that when the phrase Material having a coemcient of elasticity proportionate to pressure" is hereinbeiore or hereinafter used, it should be interpreted to mean Material such that when during operation the pressure on said material increases or decreases, its coefiicient of elasticity likewise increases or decreases but not necessarily in linear proportion to the increase or decrease of pressure on said material, no rate of increase or decrease or said, coeillcient or manner of variation of said rate with pressure on said material being excluded except as may be dictated by the particular circumstances of use of said material as a matter of design or operation."

What is claimed is:

1. In an electro-magnetic vibrator, a iluidtight casing subject to external and internal iluid pressure; means for varying and controlling said internal pressure; an electro-magnetic core; an electro-magnetic vibratory element; electro-magnetic means for superposing upon said element v an additional force component; and elastic members for mounting said element in vibratory relation with the core, said members comprising plate-like sheets embracing said vibratory element on opposite faces, one oi said sheets being in contact with the core said sheets having a coefliclent of elasticity proportionate to pressure and reacting against iiuid pressure to maintain a free vibratory relation and net mechanical stiffness between amature and core.

2. In an electro-magnetic vibrator adapted for sub-aqueous use, a' core of magnetic material; a vibratory element oi magnetic material:v electromagnetic means ior superposing a biasing magnetic ilux on said element; a housing formed with a fluid-tight chamber subject to external and internal iluid pressure; elastic means for mounting core, said means comprising a diaphragm for driving the vibratoryA element and including an elastic sheet interposed between said core and vibrating element, said sheet being in communication with said chamber and being of afrnaterial having a coefllcient of elasticity proportionate to pressure: and means for regulating the balancing pressure in said chamber against varying degrees ot external water pressure and reacting against said elastic sheet to maintain a A net mechanical stillness between the core and vibratory element.

3. An electro-magnetic s use in an aqueous medium, comprising a iluidtightcasing subjected to external and internal iluid pressure; means for varying and controlling. the internal pressure; an electro-magnetic core;

an electro-magnetic amature; electro-magnetic means for superposing upon said armature an additional force component; and elastic means interposed under positive stress between the core and armature ior retaining said armature in fluid'- said element in vibratory relation with the vibratorv ior tight and vibratory relation with the core regardless of pressure variations oi said medium. 4. In a sub-aqueous electro-magneticvibrator, `comprising in combination a huid-tight casing subjected to external and internal iluid pressure 5 and having' an acoustic chamber -formed in said casing; means ior varying and controlling the internal pressure; a magnetic core and an armature forming a magnetic circuit, said circuit being energized with magnetic flux; means for l0 mounting said armature in vibratory relation with the core and in fluid-tight communication with said chamber. said means comprising elements of elastic material and contacting said armature on its opposite faces, one element bel5 ing interposed between the core and armature and acting-to permit a free-vibration of the armature irrespectiveof the net balance o f pressure between said chamber and the external medium.

v 5. A sub-aqueous electro-magnetic vibrator including a body portion formed as a casing sub- `iected to external and internal fluid pressure and adapted to encompass a huid-tight chamber, comprising in combination a magnetic core and an armature in magnetic circuit relation. said circuit being energized with magnetic ilux; means. for varying and controlling the internal pressure; means comprising sheets of elastic material formounting vsaid amature in vibratory relation with the core, one of said sheets functioning as a diaphragm; means for retaining the shee'ts under initial pressure, and including elements to clamp said diaphragm in sealed contact with a portion ot the casing; and a channel in said casing to provide space fior expansion of the elastic material oi the diaphragm under pressure.

6. In an electro-magnetic vibrator, a huid-tight casing subject to external and internal iiuid pressure; means for varying and controlling said in- 4o ternal pressure; a core of magnetic material; a 'vibratory element of magnetic material; electromagnetic means for superposing an additional -force upon said element; and elastic material for mounting said element in vibratory relation with 5 the core, comprising a sheet functioning as a dla- -phragm and including a sheet interposed between said core and vibratory element, said sheets having the inherent quality or maintaining a free vibratory relation between said element and 50.

ing members in sheet form, one ot said members beinginterposedbetweencoreandarmature;means ior securing the other member to the casing to y form a fluid-tight chamber therein; and means to vary and control the pressure in said chamber andreacting against extraneous forces to maina5 tain a iree vibratory relation and net mechanical stiffness between armature and core over the lworking range.

8. A device of the character described, comprising a iluid-tight casing` subject to external and internal iluid pressure, said casing being formed with a chamber therein; means for varying and controlling said internal pressure; a core; an armature operative with the core; electro-magnetic means lfor a biasing magnetic ux on the amature; and means for mounting said armature in vibratory relation with the core and in fluid-tight relation with said chamber, said means including elements oi'elasticinsulating material contacting said amature on its opposite faces, one element being interposed between core and armature to. prevent adhesion of said armature under stress, and said sheets acting to maintain a net mechanical stiffness between core and armature and irrespective of the pressure of the external medium.

9. A sub-aqueous electro-magnetic vibrator comprising a fluid-tight casing subject to external and internal pressure; means for varying and oi' the armature substantially equal to the pri- 10 may magnetic repulsive force-displacement ratio of said armature.

ROGER B. COLTON. HAROLD C. MABBOTT. 

